1. Technical Field
The present application relates to a wavelength conversion element including phosphor particles and a method of manufacturing the same, and an LED element and a semiconductor laser light emitting device using the same.
2. Description of the Related Art
Conventionally, as a white LED element, a type which uses a gallium nitride (GaN)-based LED chip which emits blue light and a wavelength conversion element which is formed of a yttrium aluminum garnet (YAG) phosphor that is excited by blue light from the LED chip to emit yellow light and of a light-transmitting resin formed of a silicone resin or the like is widely known. Such a white LED element emits white light through mixture of blue light from the LED chip and yellow light emitted from the phosphor which is excited by the blue light.
In order to manufacture white LED elements having uniform chromaticity, it is necessary to cause the ratio between blue light from the LED chip and yellow light emitted from the phosphor to be constant. However, light emission nonuniformity of blue light due to LED chips is sometimes difficult to avoid in manufacturing. Therefore, it is thought that, by adjusting the wavelength conversion element in accordance with the light emission nonuniformity of blue light from the LED chip, the chromaticity of white light from the LED elements is caused to be constant.
Japanese Patent Application Laid-Open Publication No. 2004-186488 discloses a method in which, by, after a light-transmitting resin is cured, grinding a part of the light-transmitting resin layer which does not include phosphor particles until the white LED element has a target chromaticity, the path of a light beam from the LED chip is changed to adjust the chromaticity of the LED element.
Japanese Patent Application Laid-Open Publication No. 2009-231569 discloses a method of adjusting the chromaticity of a white LED element which enables adjustment of the chromaticity in various directions in chromaticity coordinates by selecting, as a second phosphor, a phosphor which has a light emission wavelength that is different from the light emission wavelength of a first phosphor and adjusting the added amount and the location of the second phosphor with respect to the light-transmitting resin.
Japanese Patent Application Laid-Open Publication No. 2009-96653 describes a problem that, when a large current is passed through the LED element in order to obtain high brightness, light and heat from the LED chip deteriorate with time the light-transmitting resin of the wavelength conversion element to lower the transmittance, and thus, the amount of light output from the white LED element is reduced, and a problem that the balance between light emitted from the LED chip and light emitted from the phosphor is lost to shift the chromaticity of the white LED element.
Japanese Patent Application Laid-Open Publication No. 2009-96653 proposes a method including, for the purpose of using glass which is excellent in resistance to heat and resistance to ultraviolet radiation as a matrix in the wavelength conversion element, a step of molding into a molded body a powder mixture of phosphor particles and glass powder, a sintering step of sintering the molded body to form a sintered body, an HIP step of processing the sintered body by hot isostatic pressing (HIP), and a processing step of processing, after the HIP step, the sintered body to obtain the wavelength conversion element. The sintering is carried out at a temperature at which a reaction between the phosphor and the glass, coloring of the glass, and the like do not occur. In the HIP step, the hot isostatic pressing is carried out at a temperature which is equal to or higher than the glass transition temperature of the glass and which is equal to or lower than the sintering temperature. With regard to the wavelength conversion element obtained in this way, the extent of reduction in light emission efficiency of the phosphor is small, and air bubble does not remain therein and the glass thereof is not colored.
In Japanese Patent Application Laid-Open Publication No. 2011-168627 (in particular, paragraphs 0028, and 0197 and 0198), after a phosphor particle layer is formed on a substrate from a solution in which phosphor particles are dispersed using electrophoresis, a light-transmitting substance to be an inorganic substance matrix is filled in spaces in the phosphor particle layer using a sol-gel method. Further, it is disclosed that the light-transmitting substance is preferably glass, and is a substance which is in a glass state and transmits light.
Japanese Patent Application Laid-Open Publication No. 2008-66365 (in particular, paragraph 0003) discloses that, when a cavity in which a light-transmitting material to be a matrix do not exist is caused in a wavelength conversion element, the existence of such a cavity attenuates light from the LED and light from the phosphor.
Japanese Patent Translation Publication No. 2011-503266 (in particular, paragraph 0002) discloses that, in an LED, ordinarily, a phosphor is embedded in a silicone resin having a refractive index of 1.4 to form a wavelength conversion element, and thus, due to the refractive index difference (0.4) between the refractive index (1.8) of the phosphor and the refractive index (1.4) of the silicone resin, a considerable ratio of light is scattered at an interface between the phosphor and the resin in the wavelength conversion element.
Further, Japanese Patent Application Laid-Open Publication No. 2011-168627 (in particular, paragraphs 0028, and 0197 and 0198) and Japanese Patent Application Laid-Open Publication No. 2011-111506 (in particular, paragraph 0027) describe that the refractive index of a phosphor which is generally used for an LED is in a range of 1.8 to 2.0. The refractive index of an yttrium aluminum garnet (YAG) phosphor is 1.8 (Japanese Patent Application Laid-Open Publication No. 2011-168627), the refractive index of a SiAlON phosphor is 1.9 (Japanese Patent Application Laid-Open Publication No. 2011-168627), and the refractive index of a CaAlSiN3 phosphor is 2.0 (Japanese Patent Application Laid-Open Publication No. 2011-111506).